Centrifugation of cells suspended in a carrier fluid in order to deposit the cells on a microscope slide for subsequent analysis is known in the field of cytology. Exemplary cell suspension fluids include normal body fluids such as synovial fluid or cerebrospinal fluid, abnormal fluids such as ascites fluid resulting from a cancer, or artificial fluids such as cell cultures. During centrifugation, the carrier fluid is forced against the slide causing cells suspended therein to attach to the slide, preferably in a substantially monolayer configuration. Subsequent processing may include staining the deposited cells with staining reagents to enhance selected cell attributes prior to microscopic analysis of the cells.
Generally, centrifugation apparatus includes an electromechanical spinner for supporting a rotor and having a motor for rotating the rotor. The rotor includes a mechanism for mounting and restraining one or more sample chambers, referred to hereinafter as cell concentrators, for rotation. The cell concentrators include generally, a chamber having a fluid receiving aperture through which a fluid specimen is added and a fluid expulsion aperture through which the fluid is expelled during centrifugation, a microscope slide disposed in fluid communication with the fluid expulsion aperture, and a securing mechanism for securing the slide to the chamber.
Since some of the materials to be centrifuged may be toxic or present a biohazard, various schemes are employed to promote the safer use of centrifuges. One technique for improving the safety of the centrifugation process is to provide a removable rotor so that the cell concentrators can be mounted in the rotor, loaded with specimens and, after centrifugation, removed from the rotor in a safe environment such as in some type of biological safety cabinet.
Bibulous paper, sometimes referred to as a filter card, is often disposed between the chamber and the microscope slide and comprises a fibrous material for absorbing carrier fluid. More particularly, the bibulous paper has an aperture aligned with the fluid expulsion aperture in the chamber so that, theoretically, fluid communication between the chamber and the slide is not impaired. However, due to the location of the bibulous paper relative to the slide, the paper may absorb the carrier fluid so rapidly that cells are absorbed and lost to analysis. Moreover, the capacity and rate of absorption of carrier fluid by the bibulous paper are difficult to control and depend on such variables as the force applied by the securing mechanism which secures the chamber to the slide, the uniformity of such force, the amount of carrier fluid, and the duration of centrifugation. Another potential drawback to the use of bibulous paper interposed between the chamber and the slide is possible contamination of the deposited cells by fibers of the paper itself. Significantly, bibulous paper has a limited fluid retention capacity. Once saturated, excess fluid in the carrier is spun off and flung at a relatively high velocity against the outside of the rotor creating potentially dangerous aerosols.
As is believed in the field of cytology centrifugation, it is desirable to keep the carrier fluid from contacting the microscope slide prior to centrifugation. Theoretically, this practice enhances the uniformity of the cell deposition and is essential where bibulous paper is inserted between the chamber and the slide since fluid contact with the bibulous paper will result in undesirable cell absorption.